Machinable high cobalt low carbon alloys for die-casting molds



Patented June 3, 1952 UNITED STATES PATENT OFFICE MACHINABLE HIGH COBALTLOW CARBON ALLOYS FOR DIE-CASTING MOLDS No Drawing. Application June 26,1950, Serial No. 170,466

9 Claims. 1

The present invention relates to machinable, high cobalt, low carbonalloys for die-casting molds and it particularly relates to die-castingmolds useful for the die-casting of. brass, aluminum and copper alloys.

It is among the objects of the present invention to provide novel, highcobalt, low carbon steels which are particularly useful in formingdie-casting molds, particularly for the die-casting of metals and havingmelting points substantially above 700 F. and not in excess of 2100 F.and with a preferred range from 1100 F. to about 1900" F.

It has been found that a rather surprising change takes place in highcobalt, low carbon steel alloys where the proportions of silicon, cobaltand carbon are controlled in definite proportions.

For example, whereas an alloy containing 0.15 to 1.60% carbon, to 3%silicon and 0 to 16% cobalt may be used quite satisfactorily in limitedvalue as a base material for die-casting molds, rather it has a veryshort life when so used and tends to crack and craze. Moreover it has tobe heat treated after machining to final form.

Surprisingly, it has been found that when the silicon content is keptbelow 1% and the cobalt content is kept from 16 to about 30%, with a lowcarbon not over 0.10% and desirably about 0.05%, that a new cobalt, lowcarbon alloy is obtained having quite remarkable properties. While it isnot suitable for a machine cutting steel, nevertheless it serves mostsatisfactorily as a steel for making die-casting molds. This type ofsteel not only is machinable after hardening, so that the necessary moldmay be readily formed, but in addition does not require anyafter-treatment. All heat treatment of this cobalt steel may be appliedbefore the machining operation.

Moreover, the alloy will give die-casting molds of extremely long life.Cracking and crazing is substantially avoided altogether, even thoughthe die-castingmold may be utilized for long periods of time.

The most satisfactory steels contain from about 0.02 to 0.05 per cent ofcarbon, about 2 to 6 per cent of chromium, about 16 to 30 per cent ofcobalt, about 2 to '7 per cent each of molybdenum and tungsten, and fromabout 0.75 to 2.5 per cent of vanadium. The molybdenum present in thesteels shall desirably exceed the amount of tungsten. Suitable resultsare had with the amount of molybdenum and tungsten substantially in theratio, of :4, and for some purposes twice the amount of molybdenum plusthe amount of tungsten shall be approximately 14.

Manganese and silicon are kept relatively low. say not over about 0.5per cent each. Likewise, phosphorus and sulfur should not exceed about.025 per cent each. The remainder of the steels is iron together withimpurities consequent upon the normal production of steels of thisgeneral type, but it will be understood that other alloying elements maybe present in amounts that do not impair the properties characteristicof the invention. Inasmuch as such impurities and additional alloyingelements exert no function influencing the invention, it may be said,for brevity, that the remainder of the steel is efiectively iron.

For most purposes the carbon content should be at the lower end of therange stated, and desirably less than about 0.05 per cent. Particularlysatisfactory results have been had from a steel of the followinganalysis:

Less than 6.1 per cent of carbon About 4 per cent of chromium About percent of cobalt About 5 per cent of molybdenum About 4 per cent oftungsten About 1.5 per cent of vanadium Steels conforming to theseproportions possess characteristics rendering them outstanding fordie-casting dies, especially for the die-casting of high melting metalsand alloys, such, for example, as copper, brass, and other copperalloys. .The tendency toward cracking or heat checking that has been aserious problem in this die casting of such materials is greatly reducedand the dies exhibit greatly improved life.

As a preferred composition of the present invention, it is particularlysuitable either for brass die-casting at 1800 to 1900 F. or aluminumdiecasting at 1100 F. to use an alloy having the following compositionin percentages by weight:

Ingredients Preferred Range Below 1 or 0.05 to 0.2. Not over 0.10 or0.10 to 0.07. Above 16 or 16 to 35.

.5to4 zws. 2to 6. .5 0.5 to 2.5. 20 to 10.

This alloy, although not satisfactory as a cutting tool, is mostsatisfactory for making diecasting molds. It may be subjected to a heat1 treatment and then machined and then after heat-treating machining, nofurther treatment is necessary. Its composition is desirably adjusted asabove to have a Brinell hardness of 440-130 490 with 477 beingpreferred. The Rock well hardness will be between 44 to 48.

Even though subjected to many thousands of die-casting operations, diesof this alloy will neither crack nor will they be deformedy 7 Althoughvarious changes maybe made in the above composition, desirably thesechanges are not productive of the most satisfactory alloy 1 and the mostdesired, unusual properties. 'For example, if the tungsten iseliminated, the cobalt carbon remaining at about 0.10%.

may be reduced between 10 to with' the factory and do not have thepeculiar efiectiveness of the preferred alloy stated above, the

following may be given:

Ingredient Percentages by Weight Carbon ..l0 12 .09 Manganese .40 36 54Silicom .81 p .88 .46 Chromium" 5. 53 5. 59 5. 56 Yan'udium 1.13 -1. 08'1.14 Molybdenum 2. 51' 2. 50 1. 20

. As typical of an alloy which although of the same general compositionis quite different from that of the present invention in having toolsteel roperties but not satisfactory die-cast steel properties, thefollowing may be given in percenta ges by weight:

Silicon up to 3% 1 Carbon 0.15 to. 1.6

Cobalt 1 to 16% Manganese 0 to 2 Chromium 0 to 15.0 Tungsten i 0.2 to 6Vanadium 0 to 5 Molybdenum "0:6 'to 3:5

It is important at all times that the carbon be kept below 0.15% anddesirably below 0.1%. It is surprising that the preferred cobalt alloyhas nocommercial .value as a high speed steel, but unexpectedly has highvalue as a die-casting steel. 1

Thedies made of a 0.05% carbon, to 30% cobalt, and 0.15% siliconSUB'EIIWillI-lot. deform under metal casting temperatures up to 2200.F..

These 00103108138615 are precipitation hardening, and in annealing themit is important to cool them in the range from 1300. to 900 F. morerapidly than prevails in furnace cooling, as by cooling in air or bysome other accelerated 'method, to avoid :the rehard'ening that wouldotherwise occur. Dies from these steels are made by machining after heattreatment. For these after many thOuSa'fl'dS 'Of operating C'Y'ClS, and

in this respect are'superiorto high speed steels that have been used forthe same purpose. They possess also other desirable physical andmechanical properties, they forge easily, and they are not difficult tomachine, even at hardnesses of 350 Brinellfi t In contrast to othersteels, the alloys of the present inventionrcontain substantially nofree carbides.

In contrast to other steels which are machined from unannealed barstock, then tempered by reheating to 1100 to 1200 C. followed byquenching in water and/or oil, the machining may take place .as a lastoperation or after heat treatment in the novel steel composition of thepresent invention.

Any chromium or vanadium may be altogether omitted without loss of thesevaluable properties. The embodiment of the invention shown and describedherein is to be considered merely as illustrative, as the invention issusceptible to variation, modification and change within the spirit andscope of the appended claims.

Having now particularly described and ascertained the nature of theinvention,'and in what manner the same is to be performed, what isclaimed is:

1. Die-casting steel of non-cutting tool steel variety, machinable afterheat treatment and highly resistant to cracking and crazing "at aluminumand brass casting temperatures of 1100 to 2200 F., containing about 0.05to 0.10 per cent of carbon, about 2 to '6 per cent of chromium, about 16to 30 per cent of cobalt, about 2 to '7 per cent of molybdenum, about0.75 to 2.5 per cent of vanadium, about 2 to 7 per cent of tungsten, andthe remainder iron.

2. Die-casting die steel of non-cutting tool steel variety, machinableafter heat treatment and highly resistant 'to cracking and crazin'g ataluminum and brass casting temperatures of 1100 F. to 2200 F.,containing about 0.02to 0.10 per cent of carbon, about 2 'to 6 per. centof chromium, about 16 to 30ipe'r cent of cobalt, about 2 to '7 per centof molybdenum, about 0.75 to 2.5 per cent of vanadium, about 2 to 7 percent of tungsten, and the remainder iron, and. the molybdenum beingpresent in an amount greater than the tungsten.

3. Die-casting die steel of non-cutting tool steel variety, machinableafter heat treatment and highly resistant to cracking and owning ataluminum and brass casting temperatures of 1100 F. to 2200"F.,,containing about 0.02 to 0.10 per cent carbon, about 2 to 6 per centof chromium, about 16 to 30 per cent of cobalt, about 2 to '7 per centofmolybdenum, about 0175 'to 2.5 per cent of vanadium, about 2 to '7percent of tungsten, and the remainder iron, and theJmolybdenum andtungsten being present in the ratio of about 5:4. I 4. Die-casting diesteel. of no eoutti'ng tool steel variety, machinable after heattreatment and wholly resistant to cracking. and orazin'g' at aluminumand brass casting temperatures of 1100 F. to 2200" F., containing notoverjabout 0.1 per cent of carbon, about 4 per cent of chromium, about25 per cent of cobalt, about 5 per cent of molybdenum, about 1.5 per.cent of vanadium, about 4 per cent of tungsten, and the remainder iron.

5. Die-casting die steel of non-cutting tool steel variety, machinableafter heat treatment and highly resistant to cracking and crazing ataluminum and brass casting temperatures of 1100" F.

to 2200 F1, containing about 0.02 1:00.15 per cent of carbon, about 2 to6 per cent of chromium, about 16 to 30 per cent of cobalt, about 2 to 7per cent of molybdenum, about 0.75 to 2.5 per cent of vanadium, about 2to 7 per cent of tungsten, and the remainder iron, and the molybdenumand tungsten being present in amounts such that twice the former plusthe latter. is about 14.

6. As a new article of manufacture, a diecasting die of non-cutting toolsteel variety, machinable after heat treatment and highly resistant tocracking and crazing at aluminum and brass casting temperatures of 1100F. to 2200 F., composed of steel containing about 0.02 to 0.10 per centof carbon, about 2 to 6 per cent of chromium, about 16 to 30 per cent ofcobalt, about 2 to 7 per cent of molybdenum, about 0.75 to 2.5 per centof vanadium, about 2 to 7 per cent of tungsten, and the remainder iron.

7. As a new article of manufacture, a diecasting die of non-cutting toolsteel variety, machinable after heat treatment and highly resistant tocracking and crazing at aluminum and brass casting temperatures of 1100F. to 2200 F.,

composed of steel containing about 0.02 to 0.10 1

able after heat treatment and highly resistant to cracking and crazingat aluminum and brass casting temperatures of 1100 F. to 2200 F.,composed of steel containing not over about 0.1 per cent of carbon,about 4 per cent of chromium, about 25 per cent of cobalt, about 5 percent of molybdenum, about 1.5 per cent of vanadium, about 4 per cent oftungsten, and the remainder Hon.

9. A machinable high cobalt low carbon mold for die casting of brass andaluminum, said alloy being devoid of cutting steel characteristics andbeing machinable after hardening, which will stand up for long periodsof time without cracking and crazing, said alloy having a siliconcontent of below 1%, a cobalt content of 16 to 30%, a carbon content ofnot over 0.1%, a chromium content of 2 to 6%, a molybdenum and tungstencontent 'each of about 2 to 7% and a vanadium content of 0.75 to 2.5%,with phosphorus and sulphur not exceeding .025%, the remainderconsisting of iron.

JOHN A. NELSON. CHARLES W. SCHUCK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,099,509 Blessing Nov. 16, 19372,201,072 Blessing May 14, 1940 2,289,449 Nelson July 14, 1942

1. DIE-CASTING STEEL OF NON-CUTTING TOOL STEEL VARIETY, MACHINABLE AFTERHEAT TREATMENT AND HIGHLY RESISTANT TO CRACKING AND CRAZING AT ALUMI NUMAND BRASS CASTING TEMPERATURES OF 1100* F. TO 2200* F., CONTAINING ABOUT0.05 TO 0.10 PER CENT OF CARBON, ABOUT 2 TO 6 PER CENT OF CHROMIUM,ABOUT 16 TO 30 PER CENT OF COBALT, ABOUT 2 TO 7 PER CENT OF MOLYBDENUM,ABOUT 0.75 TO 2.5 PER CENT OF VANADIUM, ABOUT 2 TO 7 PER CENT OFTUNGSTEN, AND THE REMAINDER IRON.